let str = 'hello'
let num = 123
let flag = false
let u = undefined
let n = null

let big = 1234n  // bigInt

let s = Symbol('1')  // 定义一个独一无二的值
let s2 = Symbol('1')


let a = '1'
let b = '1'

console.log(s == s2);


var call = function(obj) {
  let fn = Symbol('fn')
  obj[fn] = this
  obj[fn]()
  delete obj.fn
}

var obj = {
  a: 1,
  fn: 2,
  Symbol('fn'): 123,
  Symbol('fn'): ()=> {}
}
// foo.call(obj)